Summary form only given. Nonlinear optical processes in highly conductive materials, produce fast and strong changes in their refractive index. Using nano structuring, further enhancement of this Kerr-type nonlinearity, determined by free-electron dynamics in strong electromagnetic fields, can be achieved through increased light-matter interactions . However, although the initial change in optical properties occurs over femtosecond time scales, the relaxation of the excited electrons is governed by electron cooling, which may take place generally over several picoseconds. In this work, we experimentally demonstrate sub 200 fs switching of the transmission intensity due to the nonlinear spectral shift of a resonance of a specially designed metamaterial. The intensity level of transmission changes at a speed limited only by heating time of electrons as opposed to cooling (Fig. 1 A). This occurs for wavelengths longer than that of the ground state resonance and shorter than that of the spectrally shifted resonance. Further, the magnitude and sign of this modulation are seen to be highly dependent on the incident wavevector , providing an extra avenue to tailor desired optical nonlinearity (fig. 1B). This approach provides the possibility to circumvent material limitations of nonlinear response dynamics and speed up response times of nanophotonic devices.